Photodiode with decreased dark current and method for manufacturing the same

ABSTRACT

A photodiode having a reduced dark current includes a semiconductor layer, a first contact part, a second contact part, and an active region. The first contact part disposed in a first region of the semiconductor layer includes an interlayer and at least one metal layer. The second contact part disposed in a second region of the semiconductor layer includes at least one metal layer. The active region is disposed between the first contact part and the second contact part. The first contact part and the second contact part are arranged asymmetrical to each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No.10-2017-0028577 filed on Mar. 6, 2017, in the Korean IntellectualProperty Office, the disclosure of which is hereby incorporated byreference in its entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a photodiode with a decreased darkcurrent and a method for manufacturing the same, and more particularlyto a technology for reducing a dark current of a photodiode with agermanium (Ge) substrate.

2. Description of the Related Art

In an information society, semiconductors are essential elements forprocessing, storing, and converting information. A photodiode is asemiconductor device that converts an optical signal into an electricalsignal. A photodiode may be disposed in an image sensor such as a ChargeCoupled Device (CCD) or Complementary Metal Oxide Semiconductor (CMOS),and may convert received light into an electrical signal.

Meanwhile, removing a dark current increases performance of thephotodiode. The dark current may be described as a signal or currentmeasured in the absence of light energy on the photodiode, resulting inreduced accuracy of the photodiode. The dark current may cause noise ina pixel signal, such that performance of an image sensor having aphotodiode with substantial dark current is deteriorated. Therefore,many developers and companies are conducting intensive research intotechnology for removing a dark current from the photodiode.

Although special chemical processing is performed on a substrate havinga photodiode to remove a dark current, such chemical processing hasdifficulty in collecting photocharges. A technology for maintaining orimproving performance of a photodiode while simultaneously reducing darkcurrent of the photodiode, and a method for manufacturing thephotodiode, will hereinafter be described.

SUMMARY

It is an object of the present disclosure to provide a technology forreducing a dark current in a photodiode.

It is an object of the present disclosure to provide a technology forreducing a dark current by inserting an interlayer into selectedportions of an electrode layer of the photodiode.

Objects of the present disclosure are not limited to the above-describedobjects and other objects and advantages can be appreciated by thoseskilled in the art from the following descriptions. Further, it will beeasily appreciated that the objects and advantages of the presentdisclosure can be practiced by means recited in the appended claims anda combination thereof.

In accordance with one aspect of the present disclosure, a photodiodehaving a reduced dark current includes a semiconductor layer, a firstcontact part, a second contact part, and an active region. The firstcontact part disposed in a first region of the semiconductor layerincludes an interlayer and at least one metal layer. The second contactpart disposed in a second region of the semiconductor layer includes atleast one metal layer. The active region is disposed between the firstcontact part and the second contact part. The first contact part and thesecond contact part are arranged asymmetrical to each other.

In accordance with another aspect of the present disclosure, a methodfor manufacturing a photodiode having a reduced dark current includesdepositing an interlayer dielectric film over a semiconductor layeretching a first region from among the interlayer dielectric film,depositing an interlayer over the etched first region and the interlayerdielectric film, exposing the interlayer dielectric film by etching theinterlayer other than the first region, etching a second regionseparated from the first region, from among the interlayer dielectricfilm, and depositing a first metal layer over the interlayer of thefirst region, and depositing a second metal layer over the semiconductorlayer of the second region.

According to an exemplary embodiment of the present disclosure,photodiode performance can be improved by reducing a dark current of thephotodiode.

Further, according to an exemplary embodiment of the present disclosure,photodiode performance can be improved by reducing a dark current byinserting an interlayer into some parts of an electrode layer of thephotodiode.

It should be noted that effects of the present disclosure are notlimited to those described above and other effects will be apparent tothose skilled in the art from the following descriptions.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a Metal-Semiconductor-Metal (MSM)photodiode in which metal and semiconductor are arranged in anoverlapping manner.

FIG. 2A and FIG. 2B are band diagrams illustrating current generated ina photodiode.

FIG. 3 is a view illustrating a photodiode having a reduced dark currentaccording to an embodiment of the present disclosure.

FIG. 4 is a view illustrating a photodiode having an interlayerdielectric film formed of an interlayer dielectric material according toan embodiment of the present disclosure.

FIG. 5 is a view illustrating an interdigitated photodiode according toan embodiment of the present disclosure.

FIG. 6 is a view illustrating a photodiode in which contact parts of thesame type are arranged close to one another according to an embodimentof the present disclosure.

FIG. 7 is a view illustrating a Metal-Insulator-Semiconductor (MIS)photodiode according to an embodiment of the present disclosure.

FIG. 8 is a flowchart illustrating a process for manufacturing aphotodiode having a reduced dark current according to an embodiment ofthe present disclosure.

FIGS. 9 to 13 are conceptual diagrams illustrating processes forcreating a MIS photodiode according to an embodiment of the presentdisclosure.

FIG. 14 is a band diagram illustrating flow of photocharges in a MISphotodiode according to an embodiment of the present disclosure.

FIGS. 15 and 16 illustrate the magnitude of a dark current according tothickness of an interlayer according to an embodiment of the presentdisclosure.

FIGS. 17 to 20 illustrate differences in flow between a dark current anda photocurrent according to interlayer thickness.

FIGS. 21 and 22 illustrate electrical characteristics of photodiodesaccording to embodiments of the present disclosure.

DETAILED DESCRIPTION

Embodiments are described in sufficient detail to enable those skilledin the art in the art to easily practice the technical idea of thepresent disclosure. Detailed descriptions of well known functions orconfigurations may be omitted so that the gist of the present disclosureis not obscured. Hereinafter, embodiments of the present disclosure willbe described in detail with reference to the accompanying drawings.Throughout the drawings, like reference numerals refer to like elements.

The terms used in the present application are merely used to describespecific embodiments and are not intended to limit the presentdisclosure. Unless otherwise defined, all terms used herein, includingtechnical or scientific terms, have the same meanings as understood bythose skilled in the art.

A singular expression may include a plural expression unless otherwisestated in the context unless specially described. Terms defined in agenerally used dictionary may be analyzed to have the same meaning asthe context of the relevant art and may not be analyzed to have idealmeaning or excessively formal meaning unless clearly defined in thepresent application.

The embodiments of the present disclosure will hereinafter be describedcentering upon the photodiode. A photodiode may be constructed invarious ways and is not limited to the specific embodiments of thepresent disclosure. For convenience of description, photodiode havingtwo contacts are described. However, it should be understood thatembodiments of the present disclosure are described in limited detail,and that embodiments of the present disclosure are not limited to thefeatures in the following description.

FIG. 1 is a view illustrating a Metal-Semiconductor-Metal (MSM)photodiode 10 in which metal and semiconductor are arranged in anoverlapping manner. For example, semiconductor layer 11 overlaps withmetal layers of the electrodes. Referring to FIG. 1, the MSM photodiode10 includes a SiO₂ layer 11 arranged on a germanium (Ge) wafer 100. TheSiO₂ layer 11 is etched at electrode regions so that the electrodes arein direct contact with the underlying Ge substrate 100. Specifically,each electrode comprises a hole Schottky barrier layer 12 that isdisposed directly on the surface of the Ge wafer 100 in the electroderegion. A titanium (Ti) layer 13 and a gold (Au) layer 14 may bearranged over the hole Schottky barrier 12.

The germanium (Ge) MSM photodiode shown in FIG. 1 has a hole darkcurrent that directly relates to the hole Schottky barrier height. Inparticular, the hole Schottky barrier height (SBH) is inverselyproportional to dark current. In order to reduce the dark current, alarge bandgap material bay be inserted into the hole Schottky barrier 12or doping can be applied to the barrier 12, resulting in reduction ofthe hole dark current. However, inserting a large-bandgap material maycause resistance in collection of photocharges, resulting in a reducedphotocurrent.

Referring to FIG. 2A, a band diagram illustrates that a Schottky barrierheight (SBH) of a hole is relatively low at 0.56 eV. As a result, a darkcurrent (I_(dark, h)) of the hole is large as denoted by 205. Incontrast, the band diagram shown in FIG. 2B illustrates an example inwhich a Schottky barrier height (SBH) is relatively high as shown inFIG. 1. As a result, dark current in FIG. 2B is relatively low.

FIG. 2B illustrates an increased hole SBH that may be caused, forexample, by a large-bandgap material as shown in FIG. 1. As a result,dark current electron flows designated as (I_(dark, e)) and(I_(dark, h)) are reduced as denoted by 210 and 220. In contrast, whenthe Schottky barrier height is increased, resistance is introduced intothe photocurrentl, such that the photocurrent may decrease as shown inI_(photo, e), degraded 230 and I_(photo, h, degraded) 240. In otherwords, while increasing the SBH of electrodes in an MSM photodiode canreduce dark current, it also reduces photocurrent, which degradesperformance of the photodiode.

In addition, technology for reducing a dark current using doping hasdisadvantages. Doping processes are typically expensive and difficult toapply and add unacceptable cost and complexity to a process formanufacturing a photodiode.

In order to address the above-mentioned issues, a photodiode with areduced dark current and a method for manufacturing the same will bedescribed with reference to the attached drawings.

FIG. 3 is a view illustrating a photodiode having a reduced dark currentaccording to an embodiment of the present disclosure. Referring to FIG.3, view 1001 is a cross-sectional view taken along the line A-A′ of view1002, and 1002 is a top view of the photodiode. The photodiode may beclassified into first regions 1091 a and 1091 b having first contactparts, which are connected to a cathode on the semiconductor layer 1000,and second regions 1092 a and 1092 b having second contact parts, whichare connected to an anode. Accordingly, numbers 1091 and 1092 may referto both first and second regions, and the respective first and secondcontact parts disposed within those regions. An active region 1093 a maybe disposed between the first region 1091 a and the second region 1092a, and an active region 1093 b may be disposed between the first region1091 b and the second region 1092 b.

The active regions 1093 a and 1093 b may be defined by a doped portionof the substrate 1000. In some embodiments, the entire substrate 1000 isdoped, so that an entire upper surface portion of the substrate 1000 iseffectively an active region. In other embodiments, limited portions ofthe substrate are doped, such as the regions 1093 a and 1093 b that aredisposed in spaces between anode and cathode contact parts.

In the embodiment shown in FIG. 3, the anode and cathode electrodes areoffset from one another such that spaces between anode-cathode regionpairs 1091 a-1092 a and 1091 b-1092 b are less than a space betweensecond region 1092 a and first region 1091 b. The first contact partsand the second contact parts may have different structures from oneanother.

The first region 1091 a may include an interlayer 1010 a and a metallayer 1020 a. The second region 1091 b may include an interlayer 1010 band a metal layer 1020 b. First region 1091 a and second region 1091 bmay be electrically connected to each other. In other words, fingers ofan interdigitated photodiode may be constructed as seen in view 1002.

In accordance with one embodiment of the present disclosure, the cathodeelectrode includes an interlayer material that reduces a conduction bandoffset (CBO) between the semiconductor layer 1000 and each of theinterlayers (1010 a, 1010 b). In an embodiment, the interlayer materialcauses the CBO to be negligible, or zero. In other embodiments, the CBOis equal to or lower than 1.0 eV, 0.5 eV, 0.3 eV, 0.1 eV, or 0.01 eV.For example, in an embodiment in which the semiconductor layer 1000 isformed of germanium (Ge), the interlayer 1010 a or 1010 b may include amaterial such as TiO₂. In addition, the effect of reducing the darkcurrent can be enhanced by adjusting thickness of the interlayers.

In FIG. 3, each of the metal layers (1020, 1030) may comprise one ormore material layers. A material of each of the metal layers may beselected according to one or more material present in the interlayers(1010 a, 1010 b). When each of the interlayers (1010 a, 1010 b) isformed of TiO₂, each of the metal layers (1020, 1030) may be formed oftitanium (Ti). Alternatively, a lower metal layer of each of the metallayers may be formed of a first metal such as titanium (Ti), and anupper metal layer of each of the metal layers is formed of a differentmetal such as gold (Au), so that each of the metal layers (1020, 1030)includes two separate metal layers.

In various embodiments, each of the metal layers may be selected from agroup that includes gold(Au), silver(Ag), aluminum(Al), cobalt(Co),chromium(Cr), copper(Cu), gadolinium(Gd), hafnium(Hf), indium (In),iridium(Ir), magnesium(Mg), manganese(Mn), molybdenum(Mo), nickel(Ni),lead(Pb), palladium(Pd), platinum(Pt), rhodium(Rh), tantalum(Ta),titanium(Ti), tungsten(W), and zinc(Zn). In addition, a metal layer maybe formed of an alloy of one or more materials contained in theabove-mentioned group.

Alternatively, first metal layers disposed in the first regions (1091 a,1091 b), e.g. metal layers 1020, and second metal layers disposed in thesecond regions (1092 a, 1092 b) e.g. metal layers 1030, may be formed ofdifferent constituent elements, or constituent materials of the metallayers and the other metal layers may be implemented with differentcompositions. In accordance with another embodiment of the presentdisclosure, the metal layer 1020 disposed in each of the first regions(1091 a, 1091 b) may be formed of titanium (Ti), and the other metallayer 1030 disposed in each of the second regions (1092 a, 1092 b) maybe formed of gold (Au).

In an embodiment, an interlayer dielectric film formed of an interlayerdielectric material may be disposed over the semiconductor layer 1000,and the first regions (1091 a, 1091 b) and the second regions (1092 a,1092 b) may then be etched.

FIG. 4 is a view illustrating a photodiode having an interlayerdielectric film 1040 formed of an interlayer dielectric materialaccording to an embodiment of the present disclosure. FIG. 4 illustratesthe interlayer dielectric film 1040 arranged over the exposed uppersurface of Ge layer 1000. In one embodiment of the present disclosure,the interlayer dielectric film 1040 may be formed of SiO₂. Theinterlayer dielectric film 1040 may have a greater height than each ofthe interlayers (1010 a, 1010 b) so that the dielectric film overlapswith and completely covers sidewalls of the interlayers. The uppersurface of interlayer dielectric film 1040 may be disposed below uppersurfaces of each of the metal layers (1030 a, 1030 b) in the secondregions (1092 a, 1092 b), so that metal layers 1030 are exposed abovethe surface of dielectric layer 1040. In addition, the interlayerdielectric film 1040 may be coated with an anti-reflective material.

In the embodiments shown in FIGS. 3 and 4, each of the first region 1091a equipped with the interlayer 1010 a and the first region 1091 bequipped with the interlayer 1010 b may be referred to as aMetal-Insulator-Semiconductor (MIS) contact part. Each of the secondregions (1092 a, 1092 b) may be referred to as a Metal-Semiconductor(MS) contact part.

Two contact parts may be have different constituent layers because theinterlayer is disposed in only one of the contact parts.

In FIGS. 3 and 4, the CBO between the semiconductor layer 100 and eachof the interlayers (1010 a, 1010 b) may be equal to or less than apredetermined value, and a Valence Band Offset (VBO) between thesemiconductor layer 1000 and each of the interlayers (1010 a, 1010 b)may be equal to or higher than a predetermined value. For example, theVBO may be higher than about 2.9 eV, resulting in reduction of a darkcurrent. The layers may be arranged so that the CBO is minimized. Inembodiments, the CBO value is less than 1.0 eV, less than 0.5 eV, lessthan 0.3 eV, less than 0.1 eV, or less than 0.01 eV. Accordingly, insome embodiments, the CBO approaches zero. In an embodiment, whenexpressed with one significant digit, the CBO is 0.0, or zero.

FIG. 5 is a view illustrating an interdigitated photodiode that embodiesfeatures of the photodiode described with respect to FIGS. 3 and 4. FIG.5 illustrates an interlayer dielectric film 1040 surrounding aninterdigitated photodiode. In one embodiment, the interlayer dielectricfilm 1040 may be formed of SiO₂. A first connection electrode part 520and a second connection electrode part 530 may be disposed in an etchedregion of the interlayer dielectric film 1040.

The first connection electrode part 520 may be connected to a cathode,and may also be connected to one or more first contact parts (520 a, 520b, 520 c). The second connection electrode part 530 may be connected toan anode, and may also be connected to one or more second contact parts(530 a, 530 b, 530 c).

An interlayer similar to interlayer 1010 discussed above may be disposedin each of the first contact parts (520 a, 520 b, 520 c) used as the MIScontact parts. Each of the second contact parts (530 a, 530 b, 530 c)acting as the MS contact parts may not include the interlayer. Theoverlap region 1093 of the first contact parts (520 a, 520 b, 520 c) andthe second contact parts (530 a, 530 b, 530 c) may be an active region.The first contact parts (520 a, 520 b, 520 c) and the second contactparts (530 a, 530 b, 530 c) may be alternately arranged as shown in FIG.5. In another embodiment, for convenience of fabrication, the firstcontact parts (520 a, 520 b, 520 c) and the second contact parts (530 a,530 b, 530 c) may also be constructed as shown in FIG. 6.

FIG. 6 is a view illustrating a photodiode in which the same-typecontact parts are arranged adjacent to one another according to anembodiment of the present disclosure. In other words, two first contactparts (520 b, 520 c) from among the first contact parts (520 a, 520 b,520 c) may be arranged adjacent to each other, and two second contactparts (530 a, 530 b) from among the second contact parts (530 a, 530 b,530 c) may be arranged adjacent to each other. As the number ofinterdigitated photodiodes increases, a spatial margin or process marginmay be obtained in a process for depositing and etching one or moreinterlayers, when the same contact parts can be arranged adjacent toeach other.

In FIGS. 5 and 6, the first connection electrode part 520 and at leastone first contact part (520 a, 520 b, 520 c) connected thereto may havedifferent structures. In particular, the interlayer may not be disposedbelow the connection electrode part 520, and the interlayer may bedisposed only in each of the first contact parts (520 a, 520 b, 520 c).

For example, the photodiodes shown in FIGS. 5 and 6 may be constructedas follows. The photodiode may include a first connection electrode part520 connected to the cathode on a semiconductor layer 1000 (as seen inFIGS. 3 and 4) and at least one first contact part (520 a, 520 b, 520 c)connected to the first connection electrode part 520. The photodiode mayfurther include a second connection electrode part 530 connected to theanode on the semiconductor layer 1000 and at least one second contactpart (530 a, 530 b, 530 c) connected to the second connection electrodepart 530.

Each of the first contact parts (520 a, 520 b, 520 c) may include theinterlayer and at least one metal layer, and each of the second contactparts (530 a, 530 b, 530 c) may include at least one metal layer. Theabove-mentioned interlayer may not be disposed in the first connectionelectrode part 520.

As described above with respect to FIG. 3, a photodiode may beclassified into first regions, or first contact parts (1091 a, 1091 b)connected to a cathode on the semiconductor layer 1000, and secondregions, or second contact parts (1092 a, 1092 b), connected to ananode. The active region 1093 a is disposed between the first region1091 a and the second region 1092 a, and the active region 1093 b isdisposed between the first region 1091 b and the second region 1092 b.The first contact parts and the second contact parts may have differentlayer structures.

FIG. 7 is a view illustrating a Metal-Insulator-Semiconductor (MIS)photodiode 700 according to an embodiment of the present disclosure. Theview of MIS photodiode 700 illustrated in FIG. 7 is a cross-sectionalview taken along line B-B′ of FIGS. 5 and 6.

In the MIS photodiode 700, the semiconductor layer 1000 g may be formedof germanium (Ge). A cathode of the MSM photodiode 700 may include aMetal-Insulator-Semiconductor (MIS) structure formed of TiO₂.

In more detail, the SiO₂ layers (1040 a, 1040 b, 1040 c), each of whichis an interlayer dielectric film, may be disposed on the germanium (Ge)semiconductor layer 1000 g which is a Ge wafer, and TiO₂ may be formedas an interlayer material 710 a in the cathode region. When the TiO₂interlayer is present as shown in FIG. 7, dark current can be reduced.

In an embodiment in which a conduction band offset (CBO) between a TiO₂material of interlayer 710 a and the germanium (Ge) material ofsubstrate 1000 g is zero, photocharges may be effectively collectedwithout causing resistance. The hole Schottky barrier is effectivelyincreased due to large-bandgap characteristics of the TiO₂ material,resulting in reduction of a dark current. In addition, fabricationsimplicity can be maintained by not applying a doping process. A processfor inserting the TiO₂ interlayer 710 a shown in FIG. 7 will hereinafterbe described.

FIG. 8 is a flowchart illustrating a process for manufacturing aphotodiode having a reduced dark current according to an embodiment ofthe present disclosure.

Referring to FIG. 8, an interlayer dielectric film may be deposited overa semiconductor layer (S810). A first region the interlayer dielectricfilm may be etched (S820). The first region may refer to a region inwhich the interlayer will be disposed and the above-mentioned first MIScontact parts are disposed. The etching process of S820 may be a wetetching process.

An interlayer material such as TiO₂ may be deposited over the etchedfirst region and the interlayer dielectric film (S830) using, forexample, Atomic Layer Deposition (ALD). Although embodiments of thepresent disclosure use the specific example of TiO₂ as the interlayermaterial, in other embodiments, other materials with a low CBO value fora substrate interface may be used. In such embodiments, substrate andinterlayer materials may be selected to minimize the CBO value at theinterface. As an example of the deposition material, a material forallowing the CBO of the semiconductor layer to be low or zero may beused as the deposition material. A deposition process may be performedin a manner that the above exemplary material constructs the interlayer.

The interlayer other than the first region may be removed to expose theinterlayer dielectric film (S840). In an embodiment, portions of theinterlayer material that are deposited over the upper surface ofdielectric film 1040 are removed by a polishing process such as achemical mechanical polishing process (CMP). In another embodiment, theinterlayer may be removed by a dry-etch process.

The second region of the interlayer dielectric film separated from thefirst region may be etched (S850). In an embodiment, the second regionmay be wet-etched. The second region may refer to a region in which ametal material is deposited directly on the surface of the substratematerial without any intervening interlayer material.

Thereafter, a first metal layer may be selectively deposited over theinterlayer material in the first region (S860), and a second metal layermay be deposited over the semiconductor layer exposed in the secondregion (S870). When the same metal material is deposited over the firstregion and the second region, the steps S860 and S870 may be performedat the same time. In other words, in an embodiment in which differentmaterials are used for anode and cathode electrodes, the differentmaterials are deposited in separate processes. On the other hand, whenboth electrodes include the same material, it may be applied in a singledeposition process. Persons of skill in the art will recognize that themetal layers may be formed using a variety of processes, includingselective and bulk deposition and removal.

FIGS. 9 to 13 illustrate processes for forming an MIS photodiodeaccording to an embodiment of the present disclosure. The fabricationprocess of FIG. 8 will hereinafter be described with reference to FIGS.9 to 13. FIG. 9, illustrates a SiO₂ layer 1040 deposited over a Ge wafer1000 g, as disclosed in step S810 of FIG. 8. Thickness of the SiO₂ layeraccording to one embodiment may be 100 nm, and the SiO₂ layer may bedeposited, for example, using e-beam evaporator or sputtering process.

As shown in FIG. 10, a photolithography process may be performed on thedeposited SiO₂ layer 1040 to etch the SiO₂ layer, thereby forming ancathode MIS contact region 901, as explained with respect to step S820of FIG. 8. The etching may be a wet etching process performed using a1:25 diluted HF (hydrogen fluoride) solution. After etching, a portionof the Ge wafer 1000 g may be exposed as shown in region 901.

As an example of step S830 of FIG. 8, a TiO₂ layer 710 may be depositedover all exposed surfaces, as shown in FIG. 11. As an example of thedeposition process, the TiO₂ layer may be deposited using atomic layerdeposition (ALD). In an embodiment, the deposition process may beperformed at a temperature of 250° C.

As seen in FIG. 12, portions of TiO₂ layer 710 are removed from uppersurfaces of dielectric layer 1040 c as explained with respect to S840.In addition, an etching process is performed to remove a portion ofdielectric film 1040 c, thereby exposing an upper surface of substrate1000 g as described with respect to S850 of FIG. 8. In an embodiment,SiO₂ and TiO₂ materials of respective dielectric film 1040 b andinterlayer material 710 may be plasma-etched to form MS contact region902 acting as the anode region. In an embodiment, the TiO₂ layer 710 isremoved from upper surfaces of film 1040 b, thereby exposing film 1040c, while the TiO₂ layer 710 a remains in the MIS contact region 901,which is the cathode region. The TiO₂ layer remaining on dielectric film1040 b may be dry-etched using SF₆ (sulfur hexafluoride), or removed byCMP. Thereafter, for etching of the MS contact region 902 acting as thesecond region in the remaining SiO₂ layer, the wet etching process maybe performed using the HF solution as described above.

FIG. 13 illustrates an example of S860 and S870 of FIG. 8. In FIG. 13,the MIS contact region 901 acting as the cathode region in FIG. 12 andthe MS contact region 902 acting as the anode region in FIG. 12 arefilled by depositing one or more electrode metal in the respectivespaces. In an embodiment in which a plurality of electrode metalmaterials are present, each metal material may be deposited in adiscrete layer.

For example, as seen in FIG. 13, each of a first layer 521 a and asecond layer 522 a may be the cathode electrode, and each of a firstlayer 531 a and a second layer 532 a may be the anode electrode. In thiscase, the first layers (521 a, 531 a) of the respective electrodes maybe formed of titanium (Ti), and the second layers (522 a, 532 a) of therespective electrodes may be formed of gold (Au).

If an interlayer such as a TiO₂ layer is disposed only in the cathodeportion of the photodiode through the processes of FIGS. 8 to 13, holesor electrons generated by photons striking the photodiode may becollected without causing a substantial amount of resistance.

FIG. 14 is a band diagram illustrating flow of photocharges in an MISphotodiode according to an embodiment of the present disclosure. Theconcept of FIG. 14 will hereinafter be described in comparison to theband diagrams of FIG. 2. As seen at 1301 of FIG. 14, the conduction bandoffset (CBO) of TiO₂ and germanium (Ge) may be zero due to the presenceof the inserted interlayer, so that photocharges can be collectedwithout causing tunneling resistance. That is, photocharges can beeffectively collected without resistance losses.

In an embodiment that includes the MIS structure in which the TiO₂material having a large bandgap is inserted as the interlayer, the holeSchottky barrier of the cathode is greatly improved, resulting inreduction of a hole dark current of a MSM photodiode with a germaniumsubstrate. Finally, a doping process is not performed in the processdescribed with respect to FIGS. 8 to 13, such that the technologicaladvantage of fabrication simplicity of the MSM photodiode can bemaintained.

In the process of FIGS. 8 to 13, the cathode region 901 may have aMetal-Insulator-Semiconductor (MIS) contact structure, and the anoderegion 902 may have a Metal-Semiconductor (MS) contact structure.

The region 1040 b between two contacts may be an active region. In anembodiment, one or more of region 1040 b and SiO₂ regions (1040 a, 1040c) may be coated with an anti-reflective coating. In the active region1040 b, a photocurrent caused by incident light may flow between theMIS-type contact and the MS-type contact The incident light may be, forexample, infrared light. In one embodiment, the infrared light has awavelength of λ=1.55 um. However, embodiments are not limited to thisexample-in other embodiments, the infrared light may be a wavelength ina communication band such as the C band, S band or L band, or anotherwavelength.

The extent of the reduction of the dark current may be changed accordingto the height of the interlayer 710 a according to various embodiments.A detailed description thereof will hereinafter be described.

FIGS. 15 and 16 are graphs illustrating the magnitude of a dark currentaccording to thickness of the interlayer according to an embodiment ofthe present disclosure. FIGS. 15 and 16 illustrate graphs based onembodiments in which TiO₂ is included in the interlayer.

FIG. 15 illustrates I-V correlation graphs at 0 nm, 5 nm, 7 nm and 9 nm.Here, 0 nm denotes the absence of the interlayer formed of TiO₂, 5 nmdenotes that the interlayer has thickness of 5 nm, 7 nm denotes that theinterlayer has thickness of 7 nm, and 9 nm denotes that the interlayerhas thickness of 9 nm. If the TiO₂ material is disposed as theinterlayer, it can be recognized that the dark current is reducedaccording to thickness of the TiO₂ interlayer.

FIG. 16 shows a reduction of the dark current at 1V. A detaileddescription thereof. is as follows.

When the first structure having no TiO₂ (TiO₂ thickness=0 nm) iscompared with the second structure with a 5 nm interlayer formed ofTiO₂, it can be recognized that the dark current decreases by 227 timescompared to the first structure having no interlayer.

When the first structure having no TiO₂ (TiO₂ thickness=0 nm) iscompared with the structure having TiO₂ thickness of 7 nm, it can berecognized that the dark current decreases by 7,900 times compared tothe first structure having no interlayer.

Likewise, when the first structure having no TiO₂ (TiO₂ thickness=0 nm)is compared with the structure having TiO₂ thickness of 9 nm, it can berecognized that the dark current according to the embodiment decreasesby 17,000 times compared to the first structure having no interlayer.

Therefore, an interlayer of an embodiment of the present disclosure mayhave a thickness of 5 nm to 9 nm. Of course, the interlayer may beformed to have various thicknesses in various embodiments inconsideration of characteristics of the semiconductor layer, anobjective function of the photodiode, and a difference in constituentmaterials of the interlayer.

FIGS. 17 to 20 are graphs illustrating a difference in flow between adark current and a photocurrent according to the interlayer. FIG. 17shows electrical characteristics of emitted light emitted from a laserhaving a wavelength of 1.55 μm. FIGS. 17 to 20 show graphs based onembodiments in which the interlayer is formed of TiO₂.

FIG. 17 shows characteristics of the dark current and the photocurrentfor a structure having no interlayer.

FIG. 18 shows characteristics of the dark current and the photocurrentfor a structure in which the interlayer has thickness of 5 nm. FIG. 19shows characteristics of the dark current and the photocurrent for astructure in which the interlayer has thickness of 7 nm. FIG. 20 showscharacteristics of the dark current and the photocurrent for a structurein which the interlayer has thickness of 9 nm.

As seen in FIG. 17, when no interlayer material is present, the darkcurrent is relatively high, resulting in an on-off ratio of 1.04. FIG.18 shows an embodiment in which a 5 nm thick layer of TiO₂ is present,resulting in a substantially reduced level of dark current. Although thephotocurrent is also reduced at higher voltages compared to theembodiment of FIG. 17, the reduction in dark current is greater, so theon-off ratio is 8.67, which is improved compared to FIG. 17. Similarly,the embodiments of FIG. 19 and FIG. 20, which have interlayerthicknesses of 7 nm and 9 nm, respectively, have dark current reductionamounts that exceed the photocurrent reduction amounts, resulting inon-off ratios of 262 and 419, respectively. Therefore, embodiments ofthe present application are substantial improvements to conventionalphotodiode technology.

FIGS. 21 and 22 are graphs showing electrical characteristics ofphotodiodes according to embodiments of the present disclosure. Thegraphs of FIGS. 21 and 22 are obtained from embodiments in which theinterlayer is formed of TiO₂. In FIG. 21, graph 2001 shows normalizedphoto-to-dark current ratios (NPDR) for various thicknesses of theinterlayer. The graph 2002 of FIG. 22 shows NPDR based on interlayerthickness at 1V Graph 2002 shows that the NPDR of an embodiment in whicha TiO₂ interlayer is present is about 6,600 times greater than the NPDRof an embodiment in which no interlayer material is present.

In accordance with one embodiment of the present disclosure, theelectrode layers present in a cathode portion of the photodiode aredifferent from the electrode layers present in an anode portion of thephotodiode, thereby reducing dark current, resulting in increasedperformance of the photodiode.

A photodiode according to an embodiment of the present disclosure is aninterdigitated photodetector that has different types of contact parts.When the contact parts protrude from the connection electrode part in aninterdigitated structure, the interlayer may be disposed only in thecontact parts, or fingers, of the cathode, and no interlayer may bedisposed in the connection electrode portion of the cathode.

Embodiments of the present disclosure can reduce dark current byinserting an interlayer into portions of the electrode layer of thephotodiode, preserving fabrication simplicity while improving photodiodeperformance.

As is apparent from the above description, a photodiode and the methodfor manufacturing the same according to embodiments of the presentdisclosure can reduce a dark current by asymmetrically constructing anelectrode layer of a photodiode, resulting in increased photodiodeperformance.

A photodiode and the method for manufacturing the same according to anembodiment of the present disclosure can reduce a dark current byinserting an interlayer into some parts of an electrode layer of thephotodiode, resulting in increased fabrication simplicity and increasedperformance of the photodiode.

The present disclosure described above may be variously substituted,altered, and modified by those skilled in the art to which the presentinvention pertains without departing from the scope and sprit of thepresent disclosure. Therefore, the present disclosure is not limited tothe above-mentioned exemplary embodiments and the accompanying drawings.

What is claimed is:
 1. A photodiode comprising: a semiconductor layer; afirst contact part with an interlayer and at least one metal layerdisposed in a first region of the semiconductor layer, the interlayerbeing disposed between the semiconductor layer and the at least onemetal layer; a second contact part comprising at least one metal layerdisposed directly on the semiconductor layer in a second region of thesemiconductor layer; and an active region disposed between the firstcontact part and the second contact part.
 2. The photodiode of claim 1,wherein the first contact part is connected to a cathode, and the secondcontact part is connected to an anode.
 3. The photodiode of claim 1,wherein the conduction band offset (CBO) between the semiconductor layerand the interlayer is less than 1.0 eV.
 4. The photodiode of claim 1,wherein the CBO between the semiconductor layer and the interlayer isless than 0.1 eV.
 5. The photodiode of claim 1, wherein the firstcontact part is a finger of a cathode electrode of an interdigitatedphotodiode, and the second contact part is a finger of an anodeelectrode of the interdigitated photodiode.
 6. The photodiode of claim1, wherein the interlayer includes TiO₂.
 7. The photodiode of claim 1,wherein the semiconductor layer includes germanium (Ge).
 8. Thephotodiode of claim 1, further comprising: an interlayer dielectric filmdisposed over the semiconductor layer, wherein the interlayer dielectricfilm is etched in each of the first region and the second region.
 9. Amethod for manufacturing a photodiode, comprising: depositing aninterlayer dielectric film over a semiconductor layer; etching a firstregion in the interlayer dielectric film; depositing an interlayermaterial over the etched first region and the interlayer dielectricfilm; exposing the interlayer dielectric film by removing portions ofthe interlayer material disposed on the interlayer dielectric film;etching a second region separated from the first region in theinterlayer dielectric film to expose the semiconductor layer; depositinga first metal layer over the interlayer material of the first region;and depositing a second metal layer over the exposed semiconductor layerof the second region.
 10. The method of claim 9, wherein a conductiveband offset (CBO) between the interlayer material and the semiconductorlayer is 1.0 eV or less.
 11. The method of claim 9, wherein a conductiveband offset (CBO) between the interlayer material and the semiconductorlayer is 0.1 eV or less.
 12. The method of claim 9, wherein theinterlayer material includes TiO₂.
 13. The method of claim 9, wherein:etching the first region includes wet-etching the first region; andetching the second region includes wet-etching the second region. 14.The method of claim 7, wherein exposing the interlayer dielectric filmby removing portions of the interlayer material disposed on theinterlayer dielectric film includes: dry-etching the interlayermaterial.